What the Anesthesiologist Should Know before the Operative Procedure

The term "carotid stenosis" refers to partial or complete blockage of the carotid artery, most commonly secondary to atherosclerosis. Plaques are generally found at the bifurcation of the common carotid artery (CCA), encroaching into the posterior walls of the internal, external and common carotid arteries. This location may be the result of increased turbulence of flow as the larger common carotid feeds its smaller branches.

The patient with carotid disease may present with neurological symptoms, with a bruit or with an occlusion identified during a workup for another cardiovascular pathology. Neurological symptoms may be the result of emboli or a low flow state. Carotid disease is widely viewed as predictive of other cardiovascular pathologies, and patients undergoing procedures for treatment of carotid stenosis should be treated as such.

Carotid endarterectomy has been shown to be beneficial in symptomatic patients with 50-69% stenosis and highly beneficial in symptomatic patients with greater than 70% stenosis. There is no evidence to suggest that intervention is beneficial in symptomatic patients with less than 50% stenosis. In asymptomatic patients, decision to intervene should be contingent upon low surgical risk (less than 3%), and life expectancy of greater than 5 years in addition to the presence of greater than 60% stenosis.

Procedures to treat carotid stenosis include carotid endarterectomy (CEA) and its "minimally invasive" counterpart, carotid stenting. Stenting is associated with increased stroke risk relative to CEA, but with a decreased risk of myocardial infarction.

What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

As discussed above, carotid stenosis may be discovered during a workup for neurological symptoms such as stroke or TIA or during a workup for patients with coronary artery or other vascular disease. As coronary artery bypass grafting is associated with increased stroke risk in patients with neurological disease, carotid interventions may precede or coincide with cardiac surgery. Patients with neurological symptoms, particularly with symptoms escalating in frequency or severity, may be scheduled more "urgently" for surgery; however, true urgent/ emergent indications for surgery are rare; procedures done on an emergent basis have been associated with worse cardiac and neurological outcomes.

Emergent/Urgent: Indications may include acute occlusion or dissection of the carotid artery in a small minority of cases; however, most of these cases are managed medically. Recently, several small studies have suggested that there may be a role for urgent revascularization in select patients undergoing acute ischemic strokes.

Elective: Elective carotid endarterectomy may be recommended for patients with significant unilateral carotid disease, particularly in the context of neurological symptoms or other cardiovascular disease. Given that it is the rare patient with carotid plaques who does not have other cardiovascular disease, adequate knowledge of cardiac function can be critical in preparing for and planning anesthesia. Workup for neurological symptoms may also be worthwhile; however, the benefits of an extensive workup must be balanced with the risks of delaying the surgery and continued risk of a neurological event. In particular, in patients for whom CEA is a necessary predecessor to a CABG, the risk of delaying both procedures must be considered in scheduling surgery.

Preoperative evaluation

A targeted history and physical should precede anesthesia for a carotid endarterectomy. Preoperative evaluations should emphasize neurological function, particularly any history of strokes, TIAs or deficits in the MCA distribution. Workup should also emphasize cardiovascular function, given the high incidence of cardiovascular comorbidities in these patients.

Delaying surgery may be indicated if the patient shows signs and symptoms of an acute coronary syndrome.

Cardiovascular system

Acute/unstable conditions: Patients demonstrating new symptoms of ACS or new valvular dysfunction should undergo an evaluation by cardiology before undergoing surgery.

Baseline coronary artery disease or cardiac dysfunction - Goals of management: Given that risk for carotid stenosis correlates with CAD risk, a high index of suspicion for coronary artery disease is important in this patient population. Many patients are sent for carotid endarterectomy prior to undergoing CABG, as the risk of postoperative CVA in patients with greater than 75% occlusion is 15% (as compared to 0.6% in patients with no stenosis). Carotid bruits are identified predictors of aortic arch atheromas as well. Therefore, further diagnostic testing is rare in the absence of an evaluation for coronary artery disease independent of the carotid disease.

Pulmonary

Patients with pulmonary disease should be evaluated for exercise tolerance. Pulmonary function tests are not indicated in most, if not all, cases. Maintaining relative normocarbia is important intraoperatively; in patients suspected of retaining CO2, baseline arterial blood gas analysis early in the case may be worthwhile.

Renal-GI

Quantifying any degree of chronic or acute renal impairment is important for carotid endarterectomy. Drug doses and neuromuscular blocker choice should be adjusted based on anticipated clearance.

Neurologic

Preoperative workup for neurologic symptoms is very important for carotid surgery. Patients may present with preexisting deficits; it is important that these deficits be catalogued before induction of anesthesia. A thorough preoperative neurological exam both allows for postoperative comparison and can aid in determining a plan of care. In addition to working up and determining the degree of stenosis in the operative artery (usually quantified before the patient arrives for surgery), it is also crucial to determine the extent of disease in the contralateral artery, as intraoperative perfusion of the brain is dependent upon collaterals.

As discussed above, revascularization may be an appropriate option for a small subset of patients with acute stroke. For most patients, particularly at centers with little experience at operative management of acute stroke, surgery should be delayed until they have been stabilized from a neurological perspective.

In patients with chronic ischemic neurological symptoms, intraoperative management must be focused on neuroprotection, which necessarily includes maintenance of MAPs more than 20% above baseline and may extend to intraoperative placement of a shunt to enable continued perfusion. Neuromonitoring, either in the form of electroencephalography or through frequent neurological exams in the awake patient, enables the detection of changes in perfusion, but depends upon a thorough understanding of the patient's baseline. Choice of anesthetic agent (propofol being preferable to inhalation agents) and type (local/regional anesthesia is associated with improved neurological outcomes) can also be tailored based on the patient's risk of a neurologic event.

Endocrine

Avoiding hyperglycemia can help prevent ischemic damage in diabetic patients. Perioperative blood glucose monitoring and correction should be considered in these patients.

Additional systems/conditions which may be of concern

Positioning may be of concern in patients with osteoarthritis of the cervical spine and/or shoulders, particularly in awake cases, which depend on the prolonged maintenance of a supine position with the face turned away from the operative field.

What are the patient's medications and how should they be managed in the perioperative period?

The majority of the patient's prescribed medications may be continued as per usual during the perioperative period. Exceptions are, in general, discussed below. For the sake of avoiding confusion, we recommend that all herbal medications and supplements be stopped a week before surgery so that those medications that may increase bleeding (ginko, garlic, and so on) or interfere with anesthesia are cleared before the perioperative period.

Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Patients undergoing carotid endarterectomy may be on a variety of cardiac and vasoactive medications. In general, medication management should follow standard guidelines (see below), with particular attention to maintaining blood pressure, cardiac function, and normoglycemia.

What should be recommended with regard to continuation of medications taken chronically?

RenalL Discontinue diuretics on the day of surgery. Hydrochlorothiazide and triamterine used to treat hypertension may be continued.

Neurologic: Continue any home anti-epileptics or other neuroactive agents.

Anti-platelet: In theory, anti-platelet medications should be stopped 1 week preoperatively unless patient has undergone recent (within 6 months) placement of cardiac stents, in which consultation with the surgeon (and potentially cardiologist) before stopping is recommended. However, more recent evidence suggests continuation of aspirin in patients with cardiac stents. Given the extensive history of vascular disease in many carotids, the risk of bleeding must be weighed carefully against the risk of a vascular event in concurrence with the surgeon.

Hyperglycemic: Oral hypoglycemic agents should be discontinued on the day of surgery. Patients with Type 2 diabetes taking insulin may take up to one-half of their long-acting insulin on the day of surgery; patients with an insulin pump should simply maintain their basal rate.

How To modify care for patients with known allergies

The anesthesia plan for carotid surgery can easily be modified for patients with known allergies. The most common allergies seen in the perioperative realm are to latex, antibiotics and neuromuscular blockers. Specific allergies will be discussed below.

Latex allergy

If the patient has a sensitivity to latex (e.g. rash from gloves, underwear, etc.) or anaphylactic reaction, prepare the operating room with latex-free products. Latex-free catheters, gloves, and other surgical equipment are readily available at most hospitals and should be used in patients with known or suspected latex allergy.

Common antibiotic allergies and alternative antibiotics

Cefazolin is generally recommended for prophylactic antibiosis for carotid endarterectomy. In patients with penicillin or cephalosporin allergies, clindamycin or vancomycin can be used, depending on institutional preferences or protocols.

Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia

Avoid all trigger agents such as succinylcholine and inhalational agents.

Proposed general anesthetic plan: Total intravenous anesthesia (TIVA) has been demonstrated as being a safe and effective technique of general anesthesia for CEAs and could be used in this patient population. Regional anesthesia with sedation is another means of avoiding MH triggers. An MH cart with an adequate supply of dantrolene should be readily available. In any patient with a family history suggestive of MH or with a potentially predisposing condition, it is notably worthwhile to avoid general anesthesia with inhalational agents in favor of alternative options, as these alternatives (local-regional anesthesia and total intravenous anesthesia) also have both been associated with improved neurological outcomes.

Local anesthetics/ muscle relaxants

In patients with known or suspected allergies to given local anesthetics or muscle relaxants, these agents should be avoided. Patients with allergies to local anesthetics are generally allergic either to amino ester preparations or to a preservative agent used in both ester and amide preparations. In patients with identified allergies to ester preparations, amino amide preparations may be used as an alternative.

General anesthesia may be a better alternative in patients with allergies to preservatives, such as methylparaben, or for those patients for whom a specific allergen component has not been identified. Neuromuscular blocking agents are another common source of perioperative allergic reations. Neuromuscular blockade is not essential for CEA; in patients with a known allergy, neuromuscular blockers can be avoided entirely. A depolarizing agent such as succinylcholine can be used for intubation.

What laboratory tests should be obtained and has everything been reviewed?

For carotid endarterectomy, as in general, laboratory tests should only be ordered if their outcome has the potential to change management. Carotid surgery may be characterized as intermediate-risk surgery (risk of a cardiac event 1-5%); as such, it is not unreasonable that patients have a standard CBC and chemistry panel including BUN/ creatinine and glucose. Hepatic function tests may be appropriate in patients with a history of significant liver disease or of bleeding; a PT/PTT also may be useful for these patients and for patients on anticoagulation. A type and screen is not unreasonable, particularly in an anemic patient or one with significant coronary artery disease.

Preoperative EKG is appropriate for most patients; particular attention should be paid to evidence of previous MI. In patients with known pulmonary or cardiac symptoms and active symptoms of exacerbation, a chest X-ray also may be warranted.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

The major anesthetic priorities for carotid surgery are avoiding hypotension and allowing for a neurological exam during or immediately following surgery. This combination can be accomplished with either general anesthesia or regional anesthesia with light sedation. In general, patients will be supine with their head turned contralaterally to allow maximal exposure of the surgical field. Care must be taken to ensure appropriate padding of extremities. General anesthesia allows for complete airway control and complete immobilization of the surgical field; however, the ability to assess neurological function while the carotid artery is clamped is limited, even with use of EEG. Regional anesthesia is accomplished by blocking the deep and superficial cervical plexuses; it requires competency in these blocks by the anesthesiologist as well as compliance by the patient, but does enable frequent neurological examination during the case, the gold standard for assessing the impact of carotid clamping.

a. Regional anesthesia

Regional anesthesia can be accomplished with superficial and deep cervical blocks ipsilateral to the surgical site. The patient may be lightly premedicated with an anxiolytic before block placement; however, positional compliance and responsiveness are essential both for the block itself and throughout the case.

Superficial cervical blockade can be accomplished by locating the posterior border of the sternocleidomastoid muscle. After a skin wheal has been raised, the practitioner can disseminate 5 ccs of local anesthetic along the posterior and medial borders of the muscle. This block results in blockade of cutaneous nerves in the C1-C4 distribution. It can also result in unintentional blockade of the ipsilateral spinal accessory muscle, resulting in paralysis of the trapezius.

Deep cervical blockade involves targeting the C2, C3 and C4 nerve roots as they exit their cervical vertebral foraminae. With the patient positioned supine, head turned away, a line is visualized between the mastoid process and the transverse process of C6. A second line is visualized 1 cm posterior to the first line. This line is used to identify the C3 and C4 transverse processes; the C2 transverse process can be palpated 1-2 cm caudad to the mastoid process. After raising skin wheals at the individual sites, the practitioner uses needles to locate the transverse processes of the C2, C3 and C4 vertebrae. The practitioner can then walk the needle off the transverse process until paresthesias are obtained; after aspirating, inject 3-4 ccs of local anesthetic at each site.

Both procedures require technical expertise on the part of the practitioner in order to avoid the critical nervous and vascular structures of the neck.

Regional anesthesia for carotid endarterectomy confers many benefits to the patient, the primary one being ability to assess neurological function intraoperatively at different blood pressures and during different phases of the surgery. Regional anesthesia has been associated with better neurological outcomes in small studies and may decrease neurological risk to the patient by the absence of exposure to general anesthetic agents as well as by the decreased incidence of intraoperative shunt placement.

This improved neurological risk profile holds for both stents and endarterectomies. Regional anesthesia is also associated with shorter hospital stays, decreased ICU costs and decreased cardiovascular morbidity. A 2009 Cochrane meta-analysis demonstrated a nonspecific trend towards lower mortality associated with regional anesthesia, as well as a reduced need for intraoperative shunting.

Although the advantages of regional anesthesia appear manifold, evidence for most clinical outcomes is relatively weak. Regional anesthesia demands a certain level of practitioner skill as well as a compliant patient. Disadvantages for the patient include discomfort and a risk of seizures from local anesthetic exposure; the anesthesia practitioner faces patient compliance issues as well as a lack of control over the airway. The efficaciousness of regional anesthesia also depends on surgeon skill, short operative time and comfort with the notion of an "awake" patient.

b. General anesthesia

Inhalational and intravenous agents are both reasonable means of accomplishing general anesthesia in this patient population. Several small studies suggest that use of intravenous agents may be associated with better neurological outcomes than inhalational agents.

Benefits to general anesthesia include improved airway control, enhanced access to the surgical field and patient comfort. In the case of carotid surgery, where maintenance of normocarbia improves perfusion, airway control and mechanical ventilation can be extremely valuable, particularly in patients with obstructive sleep apnea and chronic pulmonary disease. The challenges of avoiding stimulating airway reflexes and inducing hypertension during intubation and extubation can be forestalled in appropriate patients with use of a laryngeal mask airway (LMA).

General anesthesia obliterates concerns about patient cooperation and about comfortable positioning; it also allows the surgeon complete access to the surgical field. A recommended technique for general anesthesia is a slow induction with neuroprotective medications (such as propofol or etomidate) and moderate opioid use. Use of total intravenous anesthesia with propofol has been associated with better neurological outcomes than use of sevoflurane; remifentanil is an attractive adjuvant for providing pain control without slowing time to emergence.

General anesthesia should be used in conjunction with specialized neurological monitors. EEG is the gold standard for intraoperative neuromonitoring in anesthetized patients, although there is evidence to suggest that somatosensory evoked potentials (SSEPs) are a slightly inferior, but also adequate, means of monitoring for ischemia after burst suppression. Neuromonitoring requires stability of anesthetic depth as well as hemodynamic stability to ensure that changes in signals correlate only with changes in cerebral perfusion.

The drawbacks of general anesthesia should be considered carefully before the decision is made to use it. Several studies have demonstrated an association between general anesthesia and worse neurological outcomes. A study involving the National Surgical Quality Improvement Project (NSQIP) Database also showed a correlation between general anesthesia and postoperative myocardial infarction, as well as a statistically insignificant increase in stroke rates and death.

What is the author's preferred method of anesthesia technique and why?

Although local-regional anesthesia appears to offer some advantages as far as neurological outcomes, it is highly dependent on both the anesthetic and the surgical operator. As such, we recommend that practitioners be facile both with LRA techniques and with nuances of GA and neuromonitoring associated with improved outcomes.

What prophylactic antibiotics should be administered?

SCIP currently recommends cefazolin 2g (3g for patients weighing more than 120 kg), to be re-dosed every 4 hours. Vancomycin and clindamycin are alternatives for patients known or suspected allergies to cephalosporins.

What do I need to know about the surgical technique to optimize my anesthetic care?

The anesthesiologist must maintain a precise awareness of intraoperative events. After making incision, the surgeon cuts through the platysma and retracts the strap muscles to expose the carotid artery, which is ensheathed with the internal jugular vein and the vagus nerve. The common, external and internal carotid branches are dissected out in this order. Dissection of the internal carotid artery can result in manipulation of the carotid body, resulting in hemodynamic changes. Instability can be preempted by injection of local anesthetic around the carotid body prior to manipulation.

The surgeon must also take particular care to avoid dislodging the plaque at this juncture. Vascular clamps are then applied to the common, followed by external and ultimately internal branches. The artery is incised and the plaque removed. Maintenance of blood pressure during clamping of the carotid artery is essential in avoiding ischemia. The surgeon may choose to place a shunt bypassing the clamped-off region if there is a change in neuromonitoring signal concerning for ischemia that cannot be corrected by increasing blood pressure. Once the plaque has been removed, the artery is repaired and the clamps removed, again sequentially; the ECA clamp is removed, followed by the CCA clamp and lastly the ICA clamp.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Close communication with the surgeon, monitoring of neurological status and blood pressure maintenance are essential. It is recommended that the anesthesiologist use pressors, inotropes or volume to maintain MAPS 20% greater than baseline during carotid clamping. There is some evidence to suggest that alpha-adrenergic agents such as phenylephrine bear increased risk of myocardial ischemia and should be avoided in these cases. The gold standard for neuromonitoring is the awake patient; in patients for whom LRA is contraindicated or inadvisable, electroencephalogram is the gold standard form of monitoring. All neuromonitoring techniques are limited by user skill, as well as by preoperative signals/exam, and poor preoperative neurological function has been associated with poor outcomes. Shunt placement should be considered in patients with changes of EEG/ SSEP signal if increasing MAP does not result in improved signal.

What are the most common intraoperative complications and how can they be avoided/treated?

Predictors of adverse outcomes include age greater than 80 years old, history of CHF, history of renal disease with a baseline creatinine greater than 2, contralateral carotid artery occlusion and ipsilateral carotid stenosis. The most common intraoperative complications of carotid endarterectomy are stroke, MI, hypertension, hyperperfusion syndrome, respiratory dysfunction and death. Although regional anesthesia shows promise as a means of decreasing neurological and cardiac risk, it does bear an increased risk of nerve injury, infection and hematoma formation at the site, as well as local anesthetic toxicity. In addition, LRA carries with it a risk of inadvertent spinal or phrenic nerve blockade.

Cardiac complications: Carotid endarterectomy is associated with a relatively high incidence of cardiac complications, with myocardial infarction being most frequent. Small studies have suggested that regional anesthesia may be associated with fewer cardiac complications than general; however, these results have not yet been corroborated by larger studies or meta-analysis. Carotid stenting is associated with a decreased incidence of cardiac complication relative to carotid endarterectomy. Hypertension is common with extubation and immediately postoperatively, and places the patient at increased risk of surgical site hematoma. Hypertension also is associated with an increased risk of cardiac and neurological complications. Carotid body hypersensitivity also may be seen in patients following carotid endarterectomy. It presents with hypotension and bradycardia, and resolves independently over time.

Pulmonary complications: Respiratory dysfunction may be seen in patients with poor neurological status or residual neuromuscular blockade. Patients with preexisting pulmonary disease may be at increased risk of postoperative respiratory dysfunction and should be closely monitored. The risk of respiratory complications may be reduced through techniques that increase patient wakefulness at emergence, such as moderate use of opioids.

Neurologic complications: Stroke is the most common neurological complication of carotid surgery. Risk factors include preoperative neurological dysfunction, contralateral carotid disease, intraoperative hypotension and/or change in EEG monitoring signal. Neuroprotective techniques include avoidance of shunting and stenting, use of neuroprotective agents such as propofol, and potentially LRA, as it allows constant monitoring of neurological status. A much less frequent neurological complication is hyperperfusion syndrome. This condition presents with severe headache, transient symptoms of ischemia and occasionally seizures and intracranial hypertension. The primary risk factor is severe hypertension; the condition usually resolves over time.

If the patient is intubated, are there any special criteria for extubation?

Minimizing coughing on and after extubation is essential for the prevention of hypertension and postoperative hematoma. Recommended techniques include deep extubation in appropriate candidates and use of opioids intraoperatively to inhibit coughing/gagging. Appropriate dosing of opioids is critical given the need to perform a neurological exam immediately after emergence.

Postoperative management

What analgesic modalities can I implement? Low-dose opioids can be used effectively for postoperative pain management. NSAIDs are not recommended in the immediate postoperative period due to the associated risk of platelet dysfunction and bleeding.

What level bed acuity is appropriate? Step-down or ICU beds are appropriate for most patients for the first 24 hours postoperatively to allow for frequent neurological checks and blood pressure monitoring.

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